# Tagged Questions

Positronium (Ps) is an unstable exotic atom bound state consisting of an electron and its anti-particle, a positron. The orbit and energy levels of the two constituent leptons are analogous to, but significantly different than those of the hydrogen atom. May also use for similar systems such as ...

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### Time and frequency extremes

I wonder if there exists a table of which physical events have the shortest time scale (like matter/antimatter annihilation) and which have the longest (like proton decay). The same question applies ...
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### Photon emission between an electron and positron

If I placed and electron and a positron at a certain distance apart in a vaccumm, they would attract each other and annihilate producing 2 or more gamma rays. But, what I would like to know is, does ...
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### Bohr's model and positronium

I was trying to get an order of magnitude estimate for the radii and energies of positronium using the Bohr's model. I did find a few places where they have used the reduced mass to replace the ...
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### What is $r$ in angular momentum quantization rule?

We know $$mvr= nh/2π$$ What is $r$ here if I consider positronium system. I suppose it should be the radius of the orbit in which both are moving. But when I take the above equation and electrostatic ...
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### How is the centre of mass of a Positronium associated with that of an electron and positron?

How is the centre of mass of a Positronium likely associated with that of an electron and positron?
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### Why does positronium decay into 2 photons more often than into 3 photons?

I cannot find the answer to the above question. I know that para-positronium is created with a probability of $25\%$ and decays into 2 photons, while ortho-positronium is created with a probability ...
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### materials that repel positrons?

In this article is discussed at some length positron formation in metallic surfaces. Positrons have work functions that describe how much energy they have to receive in order to be extracted from the ...